A considerable amount of time and effort has been expended respecting atmospheric turbulence measurement and attempts at prediction of atmospheric turbulence by many commercial, civil, and military organizations since all aircraft are affected by turbulence while they are operating. Many different sensing and signal acquisition techniques have been used, ranging from radar to laser radar, from laser velocimetry to Lidar, from hot wire anemometry to pressure tube anemometry, from passive to active acoustic sounding, from infrared to microwave radiometers, and on. Most equipment thus far is very costly, is highly complex, and is usually too large and cumbersome for general field usage or aircraft installation. Relatively little has been done respecting actual exposure monitoring of an aircraft to inflight turbulent airflow and most aircraft presently use near center-of-gravity located remote reading accelerometers for such measurements, recording continuous data on a flight recorder or its equivalent.
A summary of the current state-of-the-art of turbulent velocity measurements from aircraft, used in present day aircraft design practice, is given on pages 22, 23, 62, 63 and 170 of the book entitled "Gust Loads on Aircraft: Concepts and Applications", by Frederic M. Hoblit, published in 1988 by the American Institute of Aeronautics and Astronautics, Inc., Washington, D.C., ISBN 0-93403-45-2.
A flow direction sensor for aircraft that senses angle-of-attack and sideslip by means of a served sphere with pressure difference ports is disclosed by U.S. Pat. No. 3,079,758. Fluctuating changes in indicated attitude with respect to aircraft motion has been used in computing turbulence from the vertical and lateral components.
A ground-based air-turbulence detection system using radar techniques is disclosed by U.S. Pat. No. 3,251,057.
An airborne infrared process for spectral scanning of the atmosphere ahead of an aircraft is disclosed by U.S. Pat. No. 3,402,295. At that time it was disclosed that temperature discontinuities could be measured as an aid in locating turbulent air.
A turbulence indicator for aircraft that used inertial displacement of a mass within the indicator is disclosed by U.S. Pat. No. 3,407,668.
An airframe is an elastic non-linear mechanism and atmospheric turbulence sensing apparatus at or near the center-of-gravity or center-of-motion sees the aircraft's response to a random disturbance input through a constantly changing non-linear filter, the aircraft structure itself. Variables, such as aircraft speed, wing loading, fuel consumption, flight attitude, passenger and cargo load changes, wing lift-curve slope, and the like, all contribute to the non-linear characteristics of the elastic airframe. These variables affect the inaccuracies of an indirect measurement of turbulence exposure.
Historically, qualitative pilot reports are used to describe the characteristics of in-flight turbulence and different pilots in the same aircraft can report different results. Research turbulence instrumentation, true gust instrumentation, generally utilizes boom-mounted angle-of-attack and sideslip vanes for accurate time-histories during turbulence encounters. Such systems are not economically feasible when continuous measurement is desired during routine flight operations for long term observation of structural integrity as a contributor to flight safety. It is desirable that turbulence variations are sensed so that the aircraft operator may benefit from a time-history of the aircraft's exposure to randomly encountered turbulence during normal flight operations for the service life of the aircraft. The same aircraft type on two different repetitive routes can see wildly different total accumulated exposure to en-route turbulence. Flight over large land masses with mountain ranges and varied terrain, such as across the continental United States, can be quite different than long transoceanic flights although the flight durations may be the same. Presently, airframe useful life is determined linearly by totalizing the number of flight hours and by counting the number of takeoff-landing cycles. Inspections are carded on in linear fashion as well, ignoring the fact that the aircraft operates in a non-linear environment, a random environment biased by route structure.
Existing pitot-static airspeed sensing systems are able to sense longitudinal turbulence variations in some instances, provided that their pneumatic lines are blown clear of moisture and debris and the associated pressure transducer is sufficiently responsive. Pilot-static tube measurement of the vertical component of airspeed, from a fixed position an the airplane, is limited at best.
Turbulent atmospheric conditions also randomly exist at ground level and aircraft trailing wake vortex turbulence, shed from the aircraft during take-off and landing, is of great concern. Low level wind shear and microbursts are also of concern near and around airports and these are at the top of the list of recognized aviation hazards. An unrelated turbulent condition is found in the presence of cyclonic systems such as squall line induced vorticity, tornadoes, hurricanes and typhoons. In these instances measurements are presently made by the use of conventional anemometer wind sets and Doppler radar, if available. Conventional wind sets rely on mechanical moving components such as propellers, cups, and vanes, and are subject to overspeeding and inertial forces, and are also relatively fragile. Most are incapable of response fast enough to sense turbulence with any precision.
A primary object of the instant invention is to provide a significant improvement in the measurement of local airspeed turbulence from aircraft or on the ground and thus enable a determination of turbulence energy, or more precisely, turbulence eddy kinetic energy, and turbulence intensity.
Another object is to provide a permanent stored record of either turbulence intensity or turbulence energy in which maximum information content is preserved while a minimum of data samples are recorded.
A further object is to provide an aircraft turbulence reporting system that may be used to continuously verify the structural integrity of an aircraft airframe.
Yet a further object is to provide a simple measurement of turbulence energy in combination with a more conventional wind speed measurement.
Still another object is to provide a severe weather alarm that is triggered by a measurement of background turbulence energy exceeding a preset limit, together with wind speed.